This has to be viewed on two levels: on a buddhist cosmological level and on a secular level. I know you are secular, so you have to understand that we're not ever going to agree on this. So let's not turn this into a debate.
I hope you noticed that I never split the issue, as I invoked Kamma. So lets discuss on your terms, rebirth and kamma accepted as a given.
- On the buddhist cosmological level this life is but one in millions. And nibbana is so rare, hearing the teachings is so rare, the complete liberation from suffering so much better for me that I prefer to strive for it.
So you are willing to allow others to suffer just so you can get ahead? You would refuse to violently oppose the holocaust, allowing millions to die, so that you can reach your goal?
The obvious question is "What's in it for others?" Well, only the destruction of suffering is a permanent freedom and the supreme happiness. To help others do this, I will have to first know how to do it for myself. And the thing is that, in my view, it's best to permanently liberate a few beings from countless lives of deep suffering, than to alleviate the suffering of many without fully liberating them, because the relief is only temporary.
The problem is you dont know what those people may become, perhaps as good as a teacher as Buddha was? As you said this human life is precious, so best maintain it for as many people as we possibly can. A dictator like Hitler had practically ensured his fate if rebirth is a fact, however his victims may have become something more. I do believe that the host of this website may not be here if a pacifist attitude was taken during WW2, I probably wouldnt be either for being gay, and so we wouldnt be having this illuminating discussion.
"The only thing necessary for the triumph of evil is for good men to do nothing." - Edmund Burke
But if this "help" involves killing, then it interferes with a far superior goal: that of total and permanent liberation.
Once again, your personal peace seems to trump everything else.
If we view things in terms of Kamma, this theory doesnt necesarrily mean killing cant be justified. All it means is that certain actions have certain consequences. It seems the outcome of actions can be divorced from the morality of taking certain actions. I dont see how killing is always "wrong" If someone is willing to pay the Kammic price of generating grey kamma by killing a dictator like Hitler to save millions.